Sharjah National Oil Corporation (SNOC) operates 4 onshore gas condensate reservoirs of which 3 are very mature consisting of 50+ wells producing corrosive hydrocarbons for over 30 years. The integrity of these legacy wells is frequently questioned before any development is conceptualized, thus making it critical to evaluate the well integrity. The cost associated with pulling completions for their evaluation and running logs in all wells is significant and the availability of various emerging technologies for corrosion analysis in the market makes it challenging to choose the most reliable one. This paper focuses on the detailed analysis and comparison of electromagnetic thickness logs run in 10% of the well stock from 2016 to post-workover surface inspection of the downhole recovered tubing's in 2020/21. It also quantifies how correlating different logging technologies for well integrity increases the reliability of the electromagnetic technology applied on offset wells. The paper also showcases a comparison between mechanical and electromagnetic thickness evaluation of the production casing in-situ. Data from all the available logs from past 5 years was compiled for 6 wells. On recovery of the downhole completion tubings via a hydraulic workover, an ultrasonic (UT) inspection was performed on them at surface. Both sets of results (logs and surface inspection) were analyzed on the same logging track to give a comprehensive comparison of actual observation on surface vs the measurement by in-situ logging. Another multi-barrier corrosion and caliper log were run in the production casing to analyze their outcomes alongside older results. The final step was a comparison of all available data to create a broad well integrity profile. It was observed that the remaining production tubing metal thickness detected by electromagnetic tool (logs) and surface ultrasonic measurements were in good conformance (+/-10%). In the corrosion evaluation of the production casing, the electromagnetic tool matched extremely well with the caliper log results. This shows a large reliability of this technology to quantify corrosion in offset wells. The correlation of logs with surface inspection results across wells in the same reservoir did not indicate a strong presence of external corrosion. The study enables the management to make critical business decisions on utilizing the well stock for the future. This work is the first time a comprehensive and critical analysis on the electromagnetic thickness logging technology has been done, comparing their results of remaining wall thickness to various technologies in-situ and on surface. The analysis not only compares technology from various providers, but also mechanical vs electromagnetic measurements along with their respective advantages in quantifying well integrity assurance. The paper also gives an idea on the condition of L-80 tubulars under service for 30+ years.

This paper will share the findings of time-lapse monitoring from two corrosion surveys conducted four years apart in the subject well; present a new processing methodology that improved metal thickness estimation and yielded better results when applied to data from two legacy wells; and describe a novel surveillance tool of unique design that was also deployed in the subject well. The positive and encouraging results achieved using this tool will also be discussed. Electromagnetic pulse surveys were conducted in 2016 and 2020 to evaluate independently the metal loss in three casing barriers. The 2016 analysis involved a simplistic data processing method. A more sophisticated processing technique was recently applied to both surveys (2016 and 2020). This new method estimates the thickness for each barrier through forward modelling based on the numerical solution of the Maxwell equations. A newly introduced electromagnetic tool was also run in combination. This is a unique approach because it provides a segmented electromagnetic metal thickness evaluation of the first barrier without the need for pad contacts with the casing wall. The simplistic processing from 2016 assumed, for each barrier, a baseline for the tool readings that corresponded to the nominal casing thickness. It then translated the deflections from this baseline into a metal loss or gain. These figures were output only when they exceeded the tool's accuracy. The advanced processing that was used in 2020, which is based on forward modelling, estimated less metal loss in general in comparison with the 2016 survey. These results agreed with the segmented tool estimations for the first barrier, which was run in combination in 2020. This confirms the methodology's robustness and accuracy. In addition, this new method outputs metal loss figures at every depth point regardless of the tool accuracy. The new processing was applied to previously acquired data sets in two additional wells in the same field, and the obtained results were very satisfactory. The new tool, which provides a segmented electromagnetic metal thickness evaluation, also delivered exciting results by providing accurate thickness estimations in eight circumferential sectors of the casing wall without pad contact. This constitutes a substantial improvement over the existing all-round and averaged measurement offered by conventional electromagnetic tools. These segmented results enabled the client to make a better-informed decision about the well and to postpone an expensive workover. This paper confirms the necessity of time-lapse surveys for monitoring the integrity of downhole tubulars. It also proves that numerical solution of the Maxwell equations through forward modelling of acquired electromagnetic data yields robust and more accurate thickness estimations than the previously used methods. Finally, it demonstrates the effectiveness of the new segmented and contactless electromagnetic tool for assessing the first casing barrier.

SNOC embarked on an ambitious project to extract maximum value out of its mature fractured carbonate fields by converting them to underground gas storage facilities. This required the integration of a multitude of new and legacy data including new seismic acquisition, advanced processing and interpretation along with geophysical modelling, PVT, petrophysical and injection/pressure profiles to develop a robust reservoir model for the Moveyeid gas-condensate field. Enabling the operator to use this tool for advanced gas storage simulation predictions and to quantify risk in field development strategy to maximize condensate recovery while minimizing cushion gas volumes. Various seismic frequency cubes and survey vintages were used to delineate the Moveyeid structure and map top Shuaiba formation within the Thamama carbonates of Onshore Sharjah. Legacy wireline logs were reinterpreted using new multi-log workflows, providing inputs for static model development. As a mature field, in production for over 35+ years, cumulative produced volumes were used as an additional control, creating several iterations until achieving a match that honoured the geology. PTA, RFT and PLT were integrated in the model to quantify flow change over time. Advanced imaging revealed a north-South trending normal fault that segmented the field in to two, with all existing wells located on the up-thrown eastern block. Volumetric determination revealed that the eastern block alone was not sufficient to match hydrocarbons produced to date in any static scenario modelled. This was achieved with the inclusion of the western block and an unchanged gas-water contact. The new static model developed is more robust, with an enhanced layering configuration and property arrays that better reflect input data. Benefits were also seen during dynamic simulation where lower property multipliers were applied during history matching. Optimizing the layering and using block parallel computing power enabled the team to considerably reduce runtimes and produce an array of scenarios. The model was put to the test when the gas injection pilot project was commissioned in 2017 with low-pressure injection up to 2020, yielding a well performance accuracy within 5% of actual rates. Optimizing the strategy was essential in reducing planned cushion gas requirements by up to 20% for meeting the production target in the depleted reservoir, improving the project's capex. Utilising a combination of new and legacy data, a depleted gas-condensate carbonate reservoir has been successfully modelled. The model is being used as a tool to formulate the strategy and effectively define the field's suitability for gas storage and enhanced condensate recovery. This paper provides a case study for how these strategies can be implemented in other Middle Eastern analogues where gas storage in mature fields can act as a strategic tool for energy security.

Sharjah National Oil Corporation (SNOC) operates three onshore reservoirs in the Emirate of Sharjah. The reservoir simulation models use compositional modelling to capture the fluid dynamics in mature, low porosity highly fractured gas condensate fields. The scope of this project was to improve the reservoir characterization by investigating and overcoming lack of water production in compositional models for effective EOR and gas storage strategies. Water cut of 30%+ comprised of a combination of produced and condensed water in a reservoir with no active aquifer, thus posing a modelling challenge combined with a lack of comprehensive historical PVT data. All existing PVT reports in the database were retrieved and a comprehensive quality check was performed. The best possible PVT results for each field were short-listed and taken as reference datasets for validating the compositional EoS in a depleted field. A new EOS was generated for these fields based on legacy PVT data combined with 38+ years of production data. A shortfall of this new EOS was the inability to produce condensed water as observed in the field with Chloride counts less than 1500 ppm. To rectify this low water production mismatch, a blind test was conducted introducing water as a component in the EoS in the simulation model to see the effect. Moreover, extensive scale problems in any of the wells of 30-year-old mature assets leading to regular interventions never occurred in the asset's operational history. As expected, mobility of the fluids in the system had changed and low salinity condensed water was seen to have a good match. Liberated water was traced at the surface to confirm water production rate of the same order of magnitude as observed in production data. Due to overwhelming water production rates from the trial test, SNOC decided to perform a comprehensive extended PVT study. The naturally fractured carbonates were subjected to geological and material balance study and the data indicated an absence of active aquifers, which made it difficult to match observed water production in simulation models. To effectively plan future EOR projects like gas storage, it was necessary to model the effects of water and its interaction with injected fluids in the reservoir while honouring low water movement in the subsurface. The paper provides a novel workflow for generation of the compositional equation of state with water as a component in retrograde condensate fields. The workflow followed the lumping of hydrocarbon components to minimise runtime and capture maximum possible fluid dynamics in the reservoir without compromising the fluid properties observed in the PVT lab. It was also vital for the simulation model to honour the production history spanning over three decades. It also highlights the ability and importance of including water as an EOS component to effectively capture the condensed water in the reservoirs that many works of literature and simulators are unable to provide insight on.

Sharjah National Oil Corporation (SNOC) operates 4 onshore fields the largest of which has been in production since the 1980's. The majority of wells in the biggest field have a complex network of multilaterals drilled using an underbalanced coiled tubing technique for production enhancement in early 2000s. The scope of this project was to maximize the productivity from these wells in the late life by modelling the dynamic flow behaviour in a simulator and putting that theory to the test by recompleting the wells. A comprehensive multilateral wellbore flow study was undertaken using dynamic multiphase flow simulator to predict the expected improvement in well deliverability of these mature wells, each having 4-6 laterals (Saradva et al. 2019). The well laterals have openhole fishbone completions with one parent lateral having subsequent numerous sub-laterals reaching further into the reservoir with each lateral between 500-2000ft drilled to maximize the intersection with fractures. Complexity in simulation further increased due to complex geology, compositional simulation, condensate banking and liquid loading with the reservoir pressure less than 10% of original. The theory that increasing wellbore diameter by removing the tubing reduces frictional pressure loss was put to test on 2 pilot wells in the 2020-21 workover campaign. The results obtained from the simulator and the actual production increment in the well aligned within 10% accuracy. A production gain of 20-30% was observed on both the wells and results are part of a dynamic simulation predicting well performance over their remaining life. Given the uncertainties in the current PVT, lateral contribution and the fluid production ratios, a broad range sensitivity was performed to ensure a wide range of applicability of the study. This instils confidence in the multiphase transient simulator for subsurface modelling and the workflow will now be used to expand the applicability to other well candidates on a field level. This will result in the opportunity to maximize the production and net revenues from these gas wells by reducing the impact of liquid loading. This paper discusses the detailed comparison of the actual well behaviour with the simulation outcomes which are counterproductive to the conventional gas well development theory of utilizing velocity strings to reduce liquid loading. Two key outcomes from the project are observed, the first is that liquid loading in multilaterals is successfully modelled in a dynamic multiphase transient simulator instead of a typical nodal analysis package, all validated from a field pilot. The second is the alternative to the conventional theory of using smaller tubing sizes to alleviate gas wells liquid loading, that high velocity achieved through wellhead compression would allow higher productivity than a velocity string in low pressure late life gas condensate wells.